JP2002026651A - Oscillator and communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of an oscillation circuit and a communi cation equipment by supplying a required base correction to transistors (TRs) for the oscillation circuit so as to stabilize the oscillation and reducing the power consumption of a resistance voltage division circuit being a component of a TR base bias circuit as muck as possible while keeping a high C/N charac teristic. SOLUTION: A resonance circuit is connected to a 1st TR Q1 for oscillation purpose, the resistance voltage division circuit consisting of resistors R1, R2 is connected between a power supply Vcc and ground, an output of the circuit is given to a base of a 2nd TR Q2, an emitter of the TR Q2 is connected to a base of the TR Q1, the TR Q2 supplies a base bias current to the TR Q1, and the resistance of the resistors R1, R2 is selected higher to reduce the entire power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator used in a high-frequency circuit and a communication device provided with the oscillator.

[0002]

2. Description of the Related Art Conventionally, an oscillator in a microwave band or the like is constituted by a Colpitts oscillator or a modified oscillator thereof.

FIG. 5 shows a configuration example of a conventional oscillator. FIG.
, Q1 is an oscillation transistor, a capacitor C1 is connected between its base and emitter, a collector is grounded at a high frequency by a capacitor C7, a capacitor C6 is connected between the emitter and ground, and a base and ground are connected. And an inductive circuit is provided in a portion shown as a resonance circuit, thereby forming a Colpitts oscillation circuit.

In FIG. 5, Q2 is a buffer transistor, and supplies an oscillation signal output from the emitter of the transistor Q1 to the base of Q2 via a capacitor C2.

[0005]

In such a conventional oscillator, a voltage dividing circuit including resistors R1, R2, and R3 is provided as a base bias circuit of the oscillating transistor Q1, and a connection point between the resistors R2 and R3 is provided. The output voltage is applied to the base of Q1, and the output voltage at the node between R1 and R2 is
Is applied to the base.

When such an oscillation circuit is used in a mobile communication device such as a mobile phone, one point in design is how to suppress the overall power consumption. Conventionally, in order to reduce the overall current consumption without lowering the output level, the current (bleeder current) flowing through a resistor voltage dividing circuit (R1, R2, R3 in FIG. 5) for supplying a base bias should be minimized. It was designed to hold back. That is, generally, R1, R2, R in FIG.
If the resistance division ratio of R3 is kept constant and the combined resistance value of R1, R2, and R3 is increased, power consumption by the resistance voltage divider circuit can be suppressed accordingly.

However, as the resistance value of the resistance voltage dividing circuit is increased, the base bias current to the oscillation transistor Q1 is not sufficiently supplied, and the oscillation output level is lowered and the base bias becomes unstable. In addition, there arises a problem that the C / N characteristic of the oscillator is deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems by minimizing power consumption by a resistor voltage dividing circuit constituting a base bias circuit of a transistor and supplying a necessary base current. An object of the present invention is to provide an oscillation circuit and a communication device including the same.

[0009]

According to the present invention, a resonance circuit is connected to a first transistor for oscillation, a resistance voltage dividing circuit is connected between a power supply and a ground, and an output of the resistance voltage dividing circuit is connected. Connecting the base of the second transistor, connecting the emitter of the second transistor to the base of the first transistor,
The collectors of the first and second transistors are connected to a power supply, and an emitter current of the second transistor is supplied as a base bias current of the first transistor.

As described above, the base bias current of the first transistor for oscillation is supplied as the emitter current from the collector side of the second transistor, and the collector current of the second transistor depends on the current amplification factor of the base current. Therefore, even if the base current supplied to the second transistor is sufficiently small, a necessary base bias current for the first transistor can be supplied. Therefore, the series resistance value of the resistance dividing circuit for supplying the base bias with respect to the second transistor is set to be high, so that the power consumption by the resistance dividing circuit is extremely reduced.

Further, according to the present invention, at least a resistor is connected between the base of the first transistor and the ground, and the emitter of the first transistor is connected to the second via a capacitor.
Connected to the base of the transistor. With this configuration,
An output signal from the emitter of the first transistor, which is an oscillating transistor, is fed back to the base of the second transistor so as to operate under a high current amplification factor due to the Darlington connection between the first and second transistors. , The input impedance of the amplifier circuit including the first and second transistors is made higher. Thereby, the stability of the oscillation operation is increased.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an oscillator according to a first embodiment will be described with reference to FIGS. In FIG. 1, Q1 is a first transistor which is a transistor for oscillation, the collector of which is grounded at a high frequency by a bypass capacitor C5, a capacitor C6 between the emitter and ground, and a resonance between the base and ground. Circuits are connected to each other, and a capacitor C2 is connected between the emitter and the base via the base-emitter of Q2, thereby constituting a main part of the Colpitts oscillation circuit.

In FIG. 1, Q2 is a second transistor, the emitter of which is connected to the base of Q1. A resistor voltage dividing circuit including resistors R1 and R2 is connected between the power supply Vcc and the ground, and the divided output is supplied to the base of Q2. The collectors of Q1 and Q2 are connected to each other so that power supply Vcc is supplied. Also,
Connecting a resistor R4 between the emitter of Q1 and ground, connecting a capacitor C2 between the emitter and the base of Q2,
An oscillation output signal is extracted from the base of Q2 via the capacitor C4. Note that a capacitor C3 between the base of Q2 and the ground is provided to cut high frequency components.

In FIG. 1, an oscillation transistor Q1
Is supplied from the emitter of Q2, and this current corresponds to (base current of Q2 × current amplification factor of Q2). Since the current amplification factor of Q2 is usually several tens to several hundreds, the current supplied to the base of Q2 from the resistive voltage dividing circuit formed by R1 and R2 can be extremely small. Therefore, the output level may be reduced or the C / N
The series resistance of R1 and R2 can be set high without deteriorating the characteristics, and the bleeder current by the resistor divider circuit of R1 and R2 is sufficiently reduced to reduce the power consumption of the entire oscillator. Can be.

In the example shown in FIG. 1, the oscillation output signal from the emitter of Q1 is fed back to the base of Q2 via the capacitor C2, so that the high combined current amplification factor of Q1 and Q2 is used. The input impedance of Q1 as viewed from the resonance circuit can be increased. for that reason,
The oscillation operation is further stabilized and the C / N characteristics are improved without being affected by the fluctuation of the impedance of the circuit connected to the oscillator.

FIG. 2 is a diagram showing the configuration of the resonance circuit portion shown in FIG. Here, L1 is an inductive element such as a strip line or a chip inductor, and VD is a variable capacitance diode whose capacitance changes according to an applied voltage. L2 is an inductive element such as a strip line or a chip inductor.
Is configured to apply a control voltage thereto. At this time, the capacitor C12 grounds the high frequency component so as not to affect the oscillation frequency. The reactance of this resonance circuit is represented by the inductance of L1, the capacitance of the variable capacitance diode VD and the other capacitor C1.
0, C11, determined by the capacitance of C13,
The resonance frequency is determined by these values and the capacitance of the capacitors C2 and C6 shown in FIG. 1, and the oscillation operation is performed at the resonance frequency. Therefore, an oscillation signal having a frequency controlled by the applied control voltage is output from the base of Q2 to the outside via the capacitor C4.

Next, the configuration of the oscillator according to the second embodiment is shown in FIG. Unlike the oscillation circuit shown in FIG. 1, in this example, an oscillation output signal is extracted from the emitter of the first transistor Q1 via the capacitor C4. Even with such a circuit configuration, a predetermined base bias current can be supplied to the first transistor Q1 while the overall power consumption is reduced, and a stable oscillation signal with excellent C / N characteristics can be obtained. .

Next, FIG. 4 is a block diagram showing an example of the configuration of a communication device according to the third embodiment. In FIG.
CO is a voltage controlled oscillator. The PLL-IC is a PLL control circuit that receives an output signal of the VCO, compares the phase with the oscillation signal of the temperature-compensated crystal oscillation circuit TCXO, and outputs a control signal having a predetermined frequency and phase. V
The CO receives a control voltage at a control terminal via a low-pass filter LPF and oscillates at a frequency corresponding to the control voltage. This oscillation output signal is supplied to mixer circuits MIXa and MIXb as local oscillation signals.
The mixer circuit MIXa mixes the intermediate frequency signal output from the transmission circuit Tx and the local oscillation signal and converts the frequency to a transmission frequency signal. This signal is power-amplified by the amplifier circuit AMPa and radiated from the antenna ANT via the duplexer DPX. The signal received from the antenna ANT is amplified by the amplifier circuit AMPb via the duplexer DPX. The mixer circuit MIXb mixes the output signal of the amplifier circuit AMPb with the local oscillation signal and converts the signal into an intermediate frequency signal.
The receiving circuit Rx performs signal processing on the signal to obtain a received signal.

As the VCO in the communication device, the first
-Use the oscillator described in the second embodiment. In this manner, by using a VCO with low power consumption, a communication device with low power consumption is configured as a whole.

[0020]

According to the present invention, the base bias current of the first transistor for oscillation is supplied from the second transistor. Therefore, the series resistance value of the resistor divider for supplying base bias to the second transistor is reduced. It can be set high, which can reduce power consumption.

Also, according to the present invention, at least a resistor is connected between the base of the first transistor and the ground, and the emitter of the first transistor is connected to the base of the second transistor via a capacitor. First and second
Can be operated under a high current amplification factor due to the Darlington connection of the transistors, and the input impedance of the amplifier circuit including the first and second transistors becomes higher, thereby increasing the stability of the oscillation operation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an oscillator according to a first embodiment.

FIG. 2 is a circuit diagram of a resonance circuit portion in the oscillator.

FIG. 3 is a circuit diagram of an oscillator according to a second embodiment.

FIG. 4 is a block diagram illustrating a configuration of a communication device according to a third embodiment.

FIG. 5 is a circuit diagram showing a configuration of a conventional oscillator.

[Explanation of symbols]

 Q1-first transistor (oscillation transistor) Q2-second transistor (R1, R2) -resistor voltage dividing circuit

Claims (3)

[Claims] 1. A resonance circuit is connected to a first transistor for oscillation, and a resistance voltage dividing circuit is connected between a power supply and a ground.
An output of the resistor voltage divider is connected to a base of a second transistor, an emitter of the second transistor is connected to a base of the first transistor, and collectors of the first and second transistors are connected to a power supply. An oscillator configured to supply an emitter current of the second transistor as a base bias current of the first transistor. 2. The device according to claim 1, wherein at least a resistor is connected between the emitter of the first transistor and ground, and the emitter of the first transistor is connected to the base of the second transistor via a capacitor. Oscillator. 3. A communication device provided with the oscillator according to claim 1.